REGIONAL CEREBRAL-ARTERY MEAN FLOW VELOCITY AND BLOOD-FLOW DURING DYNAMIC EXERCISE IN HUMANS

Transcranial Doppler ultrasound-determined middle (MCA) and anterior (ACA) cerebral artery mean flow velocities (V(mean)) and pulsatility indexes (PI) were measured during "no-load" [21,60, and 102 revolutions/min (rpm)] and loaded cycling (30, 60, and 149 W) at approximately 60 rpm. At rest V(mean) MCA was 51 (36-55) cm/s (median and range; n = 10) and V(mean) ACA was 41 (36-49) cm/s (n = 7; P < 0.05). With no load on the cycle V(mean) MCA increased 4 (2-36), 10 (0-47), and 27% (4-58) (P < 0.05) at the three pedaling frequencies, respectively; arterial Pco, (Paco2) remained constant. During loaded cycling the increases were 19 (6-42), 25 (2-45), and 32% (12-67) (P < 0.01), respectively, with only a minimal change in Pa(CO2). No significant changes were observed in V(mean) ACA. Changes in V(mean) MCA were similar to those recorded by the initial slope index (ISI) of the Xe-133 clearance method (n = 11), which in turn were smaller than increases recorded by the fast-compartment flow. PI ACA followed PI MCA during no-load as well as loaded exercise and increased with work rate, perhaps reflecting an increase in pulse pressure from 56 (48-63) mmHg at rest to 109 (88-123) mmHg at 149 W (P < 0.01). Data demonstrate a graded increase in regional cerebral perfusion during dynamic exercise corresponding to the MCA territory.